A method to separate dissolved vanadium in acid solutions is presented here. These solutions or liquors may be produced, for example, during treatments for the demetallization of carbonaceous materials, such as fractions of heavy crude oils, or from residues obtained during oil refining processes, for example petroleum coke. The typical vanadium content in these liquors usually exceeds 4%, thus representing a significant source of this metal. These solutions usually contain other metals such as nickel, in concentrations around 0.1%, as well as iron, although in lesser quantities.
The recovery of vanadium from these solutions is of interest because of the diverse industrial applications of this metal, such as for catalysts in oil refining processes, the manufacture of ferrous alloys (steels), and the construction of batteries.
Processes reported in the literature for the recovery of dissolved vanadium from inorganic acid solutions involve essentially precipitation with complexing agents such as ammonia to obtain ammonium metavanadate.
These procedures generally require adjustment of the solution pH from its initial value, usually between zero and one, to a value close to two. The latter implies partial neutralization of the original acid content, meaning that the neutralized solution must be thrown away, which is not desirable.
If the acid concentration can be maintained during recovery of the metal, as with the methodology presented here, then the liquor can be used again in the initial process of demetallization. In this way, the cost associated with the overall process is reduced, and the production of waste materials that may involve environmental hazard is also reduced.
The process described here allows recovery of vanadium from solution, whatever its oxidation state, without changing the initial composition of the solution, except for the vanadium content, which decreases by about 99%. In this way, it is possible to reuse the liquor for the demetallization of carbanaceous materials, as mentioned in the previous paragraph, which provides advantages over techniques hitherto proposed in the literature.
In the process mentioned here, the recovery is carried out in a single step, and results in a ferrocyanide compound of vanadium and monovalent cation, which has practical applications in electronic devices, such as electrochromic screens. In procedures appearing in the literature, the compound formed to precipitate dissolved vanadium is ammonium metavanadate. This requires an additional step to transform it into vanadium pentoxide; this compound has known practical application and considerable commercial value. Conversion is attained heating the ammonium metavanadate in air at a temperature higher than 650 degrees Celsius.